The role of nonmuscle alpha-actinin in the attachment of actin to the plasma membrane will be investigated. Using a new procedure that we have recently developed, alpha-actinin will be purified from nonmuscle cells, including cultured fibroblasts. The properties of this protein will be studied and compared with the properties of muscle alpha-actinin. Particular attention will be paid to the interaction of this nonmuscle alpha-actinin with actin and other structural proteins. Two membrane systems will be examined: (1) The alpha-actinin in isolated plasma membranes from Hela cells will be analyzed by antibody staining of SDS polyacrylamide gels. Its association with membrane components will be studied by use of selective extraction and cleavable, chemical crosslinking reagents. Binding studies will be performed to identify potential membrane receptors for alpha-actinin. (2) Patches and caps will be isolated from lymphocytes that have been induced to patch or cap with anti-immunoglobulin. The proteins of these purified patches and caps will be analyzed by one- and two-dimensional gel electrophoresis. Through the use of cleavable, chemical crosslinking reagents we hope to determine the order of proteins linking actin to the membrane.